The proposed research examines the social-cognitive abilities enabling young children to learn the meaning of new words. A central issue for the study of early word learning is precisely how young children determine which aspect of an ongoing event is being referred to. Thus, a specific objective of the proposed studies is to determine whether and when young children interpret non-verbal behavioral cues about a person's intentions, as well as explicitly communicated information about a person's intentions, to infer the meaning of novel verbs. In study 1, 21- and 28-month-olds will be taught pairs of novel verbs using a participatory lexical training task. A unique feature of the proposed design is that the novel verb pairs will refer to three categories of events that systematically vary event appearance and the actors' intentions: events that differ in appearance, and in which the actors intentions differ; events that appear similar, but in which the actors' intentions differ; events that appear very different, but in which the actors' intentions are similar, it is expected that children's comprehension and production of the novel verbs will differ according to their ability to infer behavioral cues about the actors' intentions as an integral part of word meaning. In study 2, another sample of 21- and 28-month-olds will be taught new pairs of verbs that again systematically vary event appearance and the actors' intentions. Additionally, the verbs will refer to events involving two people. Thus, study 2 will provide unique data on the heretofore unresearched question of whether young children infer semantic intentions from participating in events involving two actors. A more long term children's health objective is to gain knowledge useful for understanding children's language and communication impairments. The proposed studies will demonstrate an ecologically valid intervention model, and provide data useful in designing meaningful interventions for children with impairments in knowledge essential for understanding other peoples' mental states and normal language acquisition.